docs: def convert(self, targetunits):
          """Set new user unit, for wavelength only.
  
          This effectively converts the spectrum wavelength
          to given unit. Note that actual data are always kept in
          internal unit (Angstrom), and only converted
          to user unit by :meth:`GetWaveSet` during actual computation.
          User unit is stored in ``self.waveunits``.
          Throughput is unitless and cannot be converted.
  
          Parameters
          ----------
          targetunits : str
              New unit name, as accepted by `~pysynphot.units.Units`.
  
          """
          nunits = units.Units(targetunits)
          self.waveunits = nunits